Generally, clay filtration is used for the removal of organic contaminants, e.g. surface active agents, which occur naturally in or are added by cross contamination with other petroleum products containing additives. The purpose of removing these surfactants is to improve the water shedding ability of, for example, a liquid fuel and to prevent those surfactants from disarming or deactivating a filter separator which would prevent its use as a filter and as a coalescer and separator of water from the fuel. Clay also is typically used for the removal of organic color bodies from the fuel. Generally, the industry has used attapulgustype clay contained in a bag or canister element in field filtering installations for turbo fuel.
A problem which has heretofore been of substantial concern in connection with clay filtration is the desire and need to measure the ongoing performance of the clay filter in the main unit and its remaining service life. When a high quality fuel is employed, fuel exiting from the filter is of a high quality and nothing is revealed as to the effectiveness of the clay as a filter. However, if a low quality fuel typically containing high surfactant levels is employed, the exiting fuel can be properly analyzed with suitable conventional instrumentation (e.g., a water separometer or a Mini-Sonic Separometer) which will assess the water shedding ability of the fuel, i.e. the ability of the water to be coalesced from the fuel. If the performance of the clay filter to remove the surfactants is poor or ineffective, then the operation must be halted and new clay filter elements installed. Prior to this invention there has been no way to predetermine the remaining clay activity before the low quality fuel is pumped through that filter.
As aviation gas turbine engines have developed there has been an increasing demand for high performance fuel, wherein the degrading effect of a small quantity of contamination will have a severe effect on fuel effectiveness. Conventional control techniques have employed a filter separator which is designed to remove entrained water and solid contaminants from the fuel. These filter separators perform their separation function (i.e., water and solids removal from the hydrocarbon fuel) by providing specific filter media for filtering solids, coalescing medium for coalescing water droplets, and a porous membrane which separates the coalesced water in the fuel. It is necessary for the coalescence to take place prior to any separation.
If the filter separator permits more than a specified amount of solids or water to pass through it to the effluent, then it has failed. Different types or modes of failure can be "mechanical" or what is commonly known as "deactivation". A mechanical failure can be attributed to improper element installation, a pinhole in a new element, or rupture of the filter separator during use. As for deactivation, this can occur even when the filter separator is mechanically sound. Present techniques do not provide for ready detection or prevention of filter deactivation which can affect either the filter coalescer cartridge or separator element without any apparent cause, indication or warning. If deactivation of either element occurs, this will allow contaminants to be passed into the aircraft with the fuel.